Add 'setup_complete' boolean to the system_settings seed data (defaults
to false) so fresh databases start in the unconfigured state.
Add two new handlers to SystemSettingsHandler:
- SetSetupComplete: marks setup_complete=true in the database
- GetSetupStatus: reads the current setup_complete value, returns
{setup_complete: bool} JSON response, defaults to false if the
setting row is missing or unparseable